In general, thermoplastic resins have relatively satisfactory impact resistance, mechanical strength, moldability, gloss, and the like. Accordingly, thermoplastic resins have been widely applied to electric components, electronic components, office equipment, automobile components, and the like.
An acrylonitrile-butadiene-styrene (ABS) resin, as a representative thermoplastic resin, includes a rubbery polymer having superior rubbery properties as a main ingredient. Here, a representative example of the rubbery polymer is polybutadiene having superior rubbery characteristics, as an impact modifier. The rubbery polymer is prepared through emulsion polymerization. The prepared rubbery polymer is mixed with an aromatic vinyl compound and a vinyl cyanide compound, followed by graft polymerization. As a result, a graft copolymer and a thermoplastic resin composition including the same may be provided.
Emulsion polymerization has advantages in that a process may be easily modified according to a primarily required quality level and, simultaneously, various products may be manufactured when a product generated in a powder form is kneaded with various matrix resins (SA, PC, PBT, PVC, and the like) and additives (a flame retardant, a weather resistant stabilizer, an antistatic agent, an antimicrobial agent, and the like) via an extrusion process.
Meanwhile, when a rubbery polymer is prepared using emulsion polymerization, polymerization time is closely related to particle size of the rubbery polymer. Particularly, a long polymerization time is required to obtain a rubbery polymer having a large particle diameter. Accordingly, to obtain a rubbery polymer having a large particle diameter within a relatively short period, a method of adding an emulsifier, a vinyl cyanide compound, and the like in small amounts before polymerization initiation, a method of continuously adding an emulsifier, and the like have been proposed. However, these methods also require a reaction time of 30 hours or more, and thus, exhibit low productivity.
In practice, when emulsion polymerization is performed under short reaction time and high reaction temperature conditions, a particle diameter of a rubbery polymer is decreased and a generation amount of a coagulated reaction product increases. In addition, reaction pressure is increased due to excessive reaction heat, whereby stability is low during a mass production process. Accordingly, it is not easy to produce a rubbery polymer having a large particle diameter at a high conversion rate within a short reaction time.
In addition, in the case of a thermoplastic resin composition prepared according to a conventional method in which a graft copolymer including a rubbery polymer having a large particle diameter is used, there is a limitation in increasing surface gloss, and impact strength decrease at low temperature is severe. To address these problems, a thermoplastic resin composition is prepared by mixing a large-diameter rubbery polymer with a small-diameter rubbery polymer. In this case, although relatively high impact strength at low temperature, and high surface gloss are exhibited, a process is complex and costs increase because a large-diameter rubbery polymer and a small-diameter rubbery polymer are separately prepared and then a mixing process is included. In addition, due to a small-diameter rubbery polymer used from an initial reaction step, there is a limitation in particle diameter control.
Accordingly, there is still a need for a graft copolymer that addresses the aforementioned disadvantages while including a large-diameter rubbery polymer and a small-diameter rubbery polymer in consideration of productivity and properties, and a technology for obtaining properties of a thermoplastic resin composition including the graft copolymer.
[Patent Document] KR0749657 B1